Sending data to logstash via tcp

The problem is that your data is already deserialized on your input and you are trying to deserialize it again on your filter. Simply remove the json filter.

Here is how I recreated your scenario:

# the json input
root@monitoring:~# cat tmp.json 
{"message":{"someField":"someValue"}}


# the logstash configuration file
root@monitoring:~# cat /etc/logstash/conf.d/test.conf
input {
  tcp {
    port => 5400
    codec => json
  }
}

filter{
}

output {
   stdout {
     codec => rubydebug
   }
}


# starting the logstash server
/opt/logstash/bin/logstash -f /etc/logstash/conf.d/test.conf


# sending the json to logstash with netcat
nc localhost 5400 <  tmp.json

# the logstash output via stdout
{
       "message" => {
        "someField" => "someValue"
    },
      "@version" => "1",
    "@timestamp" => "2016-02-02T13:31:18.703Z",
          "host" => "0:0:0:0:0:0:0:1",
          "port" => 56812
}

Hope it helps,

Don't forget to append \n at the end of your JSON:

os.writeBytes("{\"bossMessage\": {\"someField\":\"someValue\"} }" + '\n');